Test-circuit for multiple switchboards



(No Model.)

0. A. BELL.

TBSTOIRGUIT FOR MULTIPLE SWITGHBOARDS. No. 488,053. Patented Dec. 13, 18 92..

M'znesse 271 522 227::

NITED STATES PATENT FFICE.

ORO A. BELL, OF BROOKLYN, NEW YORK, ASSIGNOR TO THE WESTERN ELECTRIC COMPANY, OF CHICAGO, ILLINOIS.

TEST-CIRCUIT FOR MULTIPLE SWITCHBOARDS.

SPECIFICATION forming part of Letters Patent No. 488,053, dated December 13, 1892.

Application filed March 12, 1891. Serial No. 384,734. (No model.)

To all whom it may concern.-

Be it known that I, ORO A. BELL,a citizen of the-United States, residing at Brooklyn, in the county of Kings and State of New York, have invented a certain new and useful Improvement in Test-Circuits for Multiple Switchboards, (Case No. 1,) of which the following is a full, clear, concise, and exact description, reference being had to the accompanying drawings, forming a part of this specification.

My invention relates to multiple switchboard systems for telephone-exchanges; and its object is to provide'means whereby a line which is in use may be made to test"busy,

which means, however, shall not have any electrical connection with the telephone-line itself. y

In an application, Serial No. 379,948, filed February 3, 1891, I have described a system in which this object is attained in connection with the type of multiple switchboard known as the two-cord system, but herein I will describe a method of accomplishing the same general result in connection with the singlecord system.

My invention herein may be applied indifferently to metallic and grounded circuits.

My invention consists in improved apparatus and circuits for grounding the test-rings of the line of a calling subscriber, and provides, first, in connection with the listeningkey of a line, contacts adapted to be closed by the operation of connecting the telephone to the line and when so closed to complete a ground connection to the series of electricallyconnected test-rings of that line, so that the operator in answering a call at one board makes the line of the calling subscriber test busy at all other boards from the moment she closes her telephone to the line by operating the said key; second, in connection with the terminal plug of a line, contacts normally held open by the presence of the plug in its socket, but adapted to close a ground connection to the series of electrically-connected test-rings when the plug is withdrawn from its socket, whereby the line of the calling subscriber is put in condition to test busy as long as its terminal plug remains out of its socket.

My invention will be more clearly understood by reference to the accompanying drawings, in which- Figure 1 is a diagram of three telephonelines connected with three switchboards, with the operatorsoutlit at the last board. Fig. 2 is a longitudinal sectional view-of the plug.

The circuits connecting the several stations with the exchange are shown as metallic. The lines a and a from station 1, for example, may be traced through the line-springs and contacts of spring-jacks b b b on the first, second, and third sections of switchboard, respectively, to the annunciator c, which is bridged across between the two lines, thence to the listening-key D, where the lines are connected to the springs e 6, respectively, of the listening-key,thence to the ringing-key F, through contacts 9 g and springs 71 h, through the strands of a cord, and terminating in the sleeve and tip, respectively, of a plug I. The circuit from station 2 may be traced similarly through its line-jacks b b b at the first, second, and third boards, respectively, thence returning to its annunciator at the second board. The circuit from another station 3, which is not shown, also extends through its spring-jacks b b b at the first, second, and third boards, respectively, and returns to its annunciator at the first board. The keyboard connections of the circuits at their respective terminal boards from stations 2 and 3 are not shown, but are similar to those of lines a a, at the third board.

I will now describe briefly the novel features of my invention.

The springjacks, as 17 at the various boards are provided with test-rings j, insu lated from the linesprings k k and their contacts and furnished with normally-open contacts Z Z, which are adapted to be closed by the action of thrusting a plug into the jack.

The individual annunciators, as c, and the ringing-keys, as F, are of a type well known in the art.

The general construction of the listeningkey, as D, is also well known; but in addition to the usual springs e e and their respective contacts e a which are constructed to be closed together by the operation of throwing the cam into its vertical position, my invention provides a, spring m, insulated from but Around this core is an insulating-sleeve 1:

and outside this sleeve a tube i expanded at t for a small part of its length to the diameter of the stem or shank of the plug, the expansion forming the contact for one of the line-springs. The remainder of the stem and the body of the plug have an insulating-covering i In connection with the socket in which the terminal plug I rests when not in use my invention provides a spring 0, the curved portion of whichbears against the base of the plug I when the latter is present and is held open from its contact 19. When, however, the plug is withdrawn, the spring 0 closes uponits contact 19.

The operation of the switching system shown and of my invention in connection therewith may now be traced. Suppose that the operator at the third board sees the annunciator-shutter 0 fall. She throws the cam of her listening-key D into its vertical position, which, as described, loops her telephone into the circuit of station 1 and also closes the spring 1% against its contact, which completes an earth connection to the test-ring of the line-jacks of station 1. To this latter connection, however, I shall revert in considering the operation of testing. I

Having received the order from the calling subscriber 1, say, for a connection with subscriber 2, the operator proceeds to test to determine whether the line required is or is not busy. This she does by presenting the tip of the terminal plug I to the test-ring of switch b at her board. If now the line of the subscriber called be busy, she will perceive the characteristic sound in her telephone. Thus if the operator at the second board, at which the the from station 2 terminates, has her telcp'noneconnected to that line then the spring m of her listening-key is closed upon its contact and has closed a ground connection to the series of test-rings of the switches of line 2, as before described in connection with the operation of listening on the calling-line. Hence the battery of the testing operator, which is included in a connection from earth to the middle of her telephonecoil, finds circuit through one-half of her telephone-coil, through the contacts e e of one side of her listening-key, through the spring h and contact g of her ringing-key F, through one strand of the cord to the tip of the plug I, thence to test-ring of the tested line and to ground, as described, Again, if the second operator has completed the connection desired by subscriber 2"and thrown her listening'key into its normal condition still the terminal plug of line from station 2 is out of its socket, and hence the spring 0 is closed upon its contact and completes another ground connection to the test-rings of the switches of line 2, so that the current of an operator testing as before would find circuit as before to the test-ring of the tested line, thence through springo and contact 19 to earth. Suppose, however, that another subscriber has obtained a connnect ion with 2. Then the terminal plug and listeningkey of the latter line would not be in use; but in making the connection to the line of subscriber 2 the connecting operator would have thrust the terminal plug of the'calling subscriber into some one of the line-jacks of line'2, closing the contacts Z Z and completing a third ground connection to the test-rings of line 2, as described. This condition is shown at the third board, where the terminal plugI of line from station 1 is shown thrust into the line-jack b of'line from station 2. The battery of an operator testing would now find circuit from the tip of her testing-plug through the series of test-rings to that one at which the jack was in use, thence through contacts Z Z to ground. If the line from station 2 be not busy, then the testing operator will hear no sound in her telephone, since the test-,

rings are nowhere connected to ground. Having found that line not busy, the operator at the third board thrusts the terminal plug of line from station 1 into the line-jack b of line from station 2, raises the lever of her ringingkey F, thus disconnecting the terminal plug of line from station 1 from that line and connecting it to a calling-generator, from which the calling-current passes over the lines to station 2 and operates the call-bell provided there. The ringing-key having been returned to its normal position, the calling and answering subscribers are now in communication. Circuit may be traced from station 1 over line ITO a, through the upper line-springs and con- I tacts of its line-jacks, past the listening-key, through the contact and sprin gon the right side of ringing-key, through one strand of the connecting-cord and the tubular portion or sleeve of the terminal plug I to the upper line-spring of jack of line from station 2, thence through the upperline-springs and contacts of the linejacksof that line at the preceding boards and over one of the lines to station 2, thence returning over the other line, through the lower line-springs and contacts of the spring-jacks, through the tip of terminal plug I of line from station 1, through the corresponding strand of the cord, through the spring and contact on the left side of ringing-key, past the listening-key, through the lower contacts and springs of the line-jacks and over line a to the starting-point. Having thus traced the no electrical connection with the talking-circuit, and hence the injurious effects of the common system of putting a ground connection on one side of the line are avoided.

I do not wish to claim, broadly, a test system independent of the talking-circuits, nor the construction of the spring-j ack providdwith contacts adapted to close a test-piece to ground when a connection is made to the jack, since these have been described and claimed in Letters Patent No. 308,315, granted Milo G. Kellogg November 8, 1884; but I I claim as new and desire to secure by Letters Patent 7 1. The combination of a spring-jack having line-springs connected to the two sides of a telephone line, and a test ring insulated from the line-springs with a plug having an inner conducting-coreadapted to come into contact with one of the line-springs, a sleeve of insulating material surrounding the core, except at that portion which comes into contact With the line-spring, and a metallic tube surrounding the insulated core and terminating near the tip of the plug in an enlarged portion adapted to make contact with the other line-spring and having an insulating-covering surrounding it for such portion of its length as to prevent its coming in contact with the testring of the jack, in the manner and for the purpose specified.

2. In a listening-key for telephone-exchange systems, the combination of normally-open contacts adapted when closed to connect the operators telephone to a subscribers line, means for closing the contacts, a test-ring and ground connection therefrom, and contacts in said ground connection closed by the act of connecting the operators telephone to line, substantially as specified.

3. The combination, with telephone-lines extending from the subscribers station through the line springs and contacts, of

spring-jack switches provided with test-rings insulated from the line-springs, respectively, thereof, the testrings of the spring -jack switches of each line being electrically coned to be inserted in the spring-jack switch of 'the other line to loop the two lines together,

of a listening-key provided with contacts, one of which is connected to earth and the other to the series of test-rings of the lines, and a socket adapted to receive the plug when not in use, said socket being provided with normallyopen contacts, said contacts being adapted to close together upon the removal of the plug from the socket and to connect the test-rings of the switches to earth, substantially as specified.

5. The combination, with a spring-jack having two linesprings and a test-ring insulated from said line-springs, of a connecting-plug having a centralcore furnished with a tip making contact with one of said line-springs, a conducting-sleeve insulated from the core and making contact with the other of said linesprings, and a sleeve insulating the said conductingsleeve from the test-ring, substantially as and for the purpose specified.

In witness whereof I hereunto subscribe my name this 27th day of February, A. D.l891.

0R0 A. BELL.

Witnesses:

FRANK PIERSON, JOHN O. PARSONS. 

